Mayo Belwa, a highly shocked enstatite achondrite, fell during the evening of 3 August 1974 in the Adamawa District, NE. Nigeria (8° 58' N., 12° 05' E.). The stone weighed 4·85 kg and was deposited in the Geological Survey of Nigeria and loaned for study to the British Museum (Natural History). It is composed principally of enstatite (0·02 FeO%), with some olivine (Fo100), diopside, feldspar (An9 Ab88 Or3), and minor Fe-Ni metal and the sulphides oldhamite, daubréelite, ferroan alabandine, and troilite. The kamacite contains between 0·15% and 1·2% Si and the troilite contains 1·1% Ti. The meteorite possesses vuggy cavities, which contain fluor-amphibole needles projecting from their walls, suggesting the presence at some time of a volatile-rich phase. The titanium-rich troilite, the nearly ironfree enstatite and the Mg/Si ratio are typical of the E-achondrites.

Smolyaninovite, (Co, Ni, Ca, Mg)3 (Fe, Al)2 (AsO4)4. 11H2O, has recently been recognized in the mineralized region around Mount Cobalt, Queensland. It is a soft polycrystalline earthy yellow-brown material, is probably the weathering product of cobaltian arsenopyrite or alloclase, and shows para-magnetic properties.

Gypsum and anhydrite from the Neogene of the central Jordan valley associated with basalt bodies in the Menahamiya area contain abundant euhedral magnetite and diopside crystals and rarer grossular. The original calcareous shales above the gypsum were transformed into hydrogrossular cemented by secondary calcite and gypsum. The mineralization is assumed to be due to low-temperature, high water-pressure metasomatic activity similar to the process of rodingization. The described occurrence is unusual in that the hydrothermal solutions may have been partly formed in situ by thermal dehydration of the gypsum. In a nearby locality, Tel Shaharit, the mineralization occurred in a calcareous environment producing thomsonite, natrolite, and hydrogrossular.

During the summer of 1967 willcmite was found for the first time in the Ilímaussaq alkaline intrusion, South Greenland. The willemite occurs in an albitite together with aegirine/acmite, albite, analcime, arfvedsonite, apatite, chkalovite, hemimorphite, microcline, monazite, natrolite, naujakasite, neptunite, sphalerite, and polylithionite. Analytical, optical, and X-ray data were obtained from the willemite. Willemite from a calcite vein at Franklin Furnace, New Jersey, and from a quartz vein at Mussartût, South Greenland, were also examined.

One of the willemite crystals from Ilimaussaq was a trilling on <100>. This is the first time willemite has been found as a trilling.

Motukoreaite occurs as relatively abundant, white, clay-like cement in both beach-rock and basaltic volcanic tuffs on the flanks of a small, extinct, late Pleistocene, basaltic cone at Brown's Island (Motukorea), within Waitemata Harbour, Auckland, New Zealand (36° 50′ S., 174° 35′ E.). The occurrence was originally recorded by Bartrum (1941) as ‘beach limestone’ found at two places of the island's shore. The beach-rock consists of a grain-supported fabric of poorly sorted, well-rounded, alkali-olivine basalt pebbles and granules, subangular to sub-rounded fresh olivine sand and abraded sand- and gravel-sized bioclasts in a colourless to pale yellow-green aphanocrystalline matrix of motukoreaite. Additional detritals include quartz, feldspar, and sedimentary rock fragments. Stereoscan examination of the surface of pieces of the cement prised from the beach-rock showed a box-work of plate-like crystals with a hexagonal form in which individuals measured about 3×3×0·02 microns (fig. 1).

Wet-chemical analysis of a separate of the cement containing some 5 % quartz and traces of calcite and goethite gives SiO2 5·55, Al2O3 17·87, Fe2O3 0·73, CaO 0·92, MgO 22·98, MnO 0·70, ZnO 0·56, Na2O 0·71, K2O 0·10, CO2 9·32, SO3 10·00, H2O+ 19·62, H2O- 10·35, sum 99·41 %. The unit-cell formula using obtained unit-cell constants and measured specific gravity 1·43) is (Na0·73K0·07)∑0·80(Mg18·13Mn0·32Zn0·21)∑18·66Al11·15(CO3)6·22(SO4)3·97 (OH)51·1927·20H2O. Of several idealized formulae that may be proposed NaMg19Al12(CO3)6.5 (SO4)4(OH)54·28H2O is preferred.

Microprobe and X-ray investigation of a mineral occurring with breithauptite, nickeline, and other arsenides in the naujaite at Igdlúnguaq, Ilímaussaq alkaline massif, S. Greenland, shows that this mineral, which was formerly misidentified as ‘maucherite’, is a westerveldite (Fe0·85Ni0·15)As, of much iron-richer composition than the nickeloan westerveldites from the only two other known occurrences of this mineral. Westerveldite from Igdlúnguaq was presumably formed by reaction of nickeline with iron-rich solutions under conditions of reheating at temperatures of about 450° C and under partial pressures of arsenic below those necessary to stabilize nickeline. Sulphur-bearing löllingite occurs as exsolution blades in the westerveldite. Iron-rich nickeline, up to a composition (Ni0·82Fe0·18)As0·95Sb0·05, was presumably formed by recrystallization of nickeline in the transition stage just before this mineral became unstable and was replaced by westerveldite.

Fassaitic diopside containing 22–23 wt% Al2O3 (approximately 41–43% calcium Tschermak's molecule, CaAl2SiO6) and melilite containing 69–43% gehlenite crystallized from a blast-furnace slag at atmospheric pressure between about 1450°C and 1250°C. The occurrence is of petrological interest because the association of pyroxene with gehlenite-rich melilite has not been recorded from experimental studies in the system CaO-MgO-Al2O3-SiO2, and because of the similarity of the compositions of both minerals to pyroxene and melilite in the Ca-Al-rich inclusions of the Allende meteorite.

Basalt composition is defined as that chemical composition which when crystallized at one atmosphere under standard conditions will yield olivine, clinopyroxene, and plagioclase as the principal silicate phases. This gives six classes of basalt defined by their order of crystallization but only four of these are encountered in rocks: class 1, olivine→clinopyroxene→plagioclase; class 2, olivine→plagioclase→clinopyroxene; class 3, plagioclase→olivine→clinopyroxene; and class 4, plagioclase→linopyroxene→olivine. Classes 5 and 6 would have clinopyroxene as the first phase. The class can be determined from the rock composition from multivariate discriminant function equations but Si, Mg, Al, and Na provide a more simple diagnosis via dis-criminant diagrams. Rock series plotted on these diagrams show systematic trends that allow the series them-selves to be classified. Each class corresponds with a commonly recognized basalt type and all four classes relate to tectonic setting groups.

The stratigraphical limits on the age of the Freetown intrusion, Sierra Leone, are very wide, yet the intrusion has not previously been accurately dated by isotopic methods, despite a number of attempts. Rubidium-strontium dating of acid veins contemporaneous with the early stages of the prolonged cooling history of the intrusion provides an age of 193 ± 3 Ma. The veins consist of quartz and orthoclase with relict minerals, principally plagioclase, from thehost gabbro. Electron-microprobe analysis of the altered minerals of the veins, and the petrography of the vein and adjacent host gabbro clearly demonstrate that the veins were formed from a granitic fraction, differentiated in situ from the surrounding solid gabbro with the assistance of a hydrous fluid phase within the incipient vein. This assertion is supported by the identical, low value of the initial 87Sr/86Sr ratio (0·70389) obtained from both the acid and basic rocks, and the technique described here may be useful in dating other, similar, intrusions.

The second occurrence of pyrobelonite, MnPb(VO4)(OH), first recorded at långban, Sweden, is reported. It was found with other manganese and iron minerals at the site of an abandoned 19th-century manganese mine at Tŷ Coch near South Cornelly, Mid Glamorgan, Wales. Reflectance values for pyrobelonite from Tŷ Coch, topotype material from Långban, and for two of the minerals associated with pyrobelonite at Tŷ Coch, vanadinite and hausmannite, are given. Electron-probe analyses of pyrobelonite from both localities give results that are in good agreement with its theoretical composition but disagree with the only previous published analysis.

The plagioclase-alkali-feldspar geothermometer formulated by Stormer (1975) does not take into account the effect of small amounts of calcium in the alkali feldspar. This geothermometer has been reformulated using ternary regular solution model equations, and it is shown that as the Ca content of the alkali feldspar increases the temperature calculated using the Stormer geothermometer will be increasingly too high.

Phosphate minerals are widespread minor constituents of the pallasites. Both anhydrous primary and hydrous decomposition/alteration phosphates occur. The primary minerals, in decreasing order of abundance, are whitlockite, stanfieldite, and farringtonite, as well as a possibly new phosphate. The decomposition phosphates are compositionally heterogeneous and thus complex. Some may be new minerals. The phosphate minerals serve as the major repository for the alkali elements in pallasites, with individual crystals containing up to several percent of Na+K. Equilibrium established between coexisting phosphide and phosphate defines a relatively narrow range of ƒO2 values.

Petrography of an original websterite from Jotunheimen shows evidence of plagioclase exsolving from clinopyroxene to form both internal lamellae and also an intergranular symplectite with olivine and magnetite hercynite. The olivine is secondary, forming from both clinopyroxene and orthopyroxene. Microprobe chemical analyses are presented of all the phases mentioned. From the ratio of plagioclase to clinopyroxene the initial clinopyroxene probably formed at a depth greater than 35 km; if it crystallized at magmatic temperatures (1150°C) the depth must have been about 70 km. Exsolution took place at a pressure less than 6 kb after upthrusting of the rock to shallower depths. The great depth of initial crystallization has important implications for the conditions of origin of the ultramafic component of this granulite facies terrain.

Equilibrium thermodynamic methods are used to develop an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964). The geothermometer and oxygen barometer are presented graphically for coexisting ilmenite solid solution and magnetite solid solution in the system FeO-Fe2O3-TiO2. Equations are also given for calculating temperature and oxygen activity for natural coexisting iron-titanium oxides containing other components. Large departures in composition from the system FeO-Fe2O3-TiO3 result in large uncertainties in the calculated temperature and activity of oxygen.

Published analyses for 14 trace and minor siderophilic elements have been interpreted to indicate a close relationship between the IIIAB iron meteorites and the main group of pallasites. These two groups respectively account for about 32 and 75 % of all irons and pallasites. The composition of the metal in the main group pallasites is very close to that calculated for the liquid after 80 % of a IIIAB iron melt has fractionally crystallized. The pallasites probably formed by the intrusion of residual molten metal from the core into a surrounding olivine mantle.

The formation of ilmenite from titanomagnetite frequently shows separate generations of production. The ilmenite products can be combined with the magnetite host to represent the intermediate stages in this development. Use of the Buddington and Lindsley (1964) geothermometer in conjunction with this method provides a number of points in the temperature and oxygen-fugacity history of a single, complex magnetiteilmenite grain.

Application of the method is illustrated by an example from the Freetown layered gabbro. A titanomagnetite exsolved granular ilmenite whilst cooling and this process ceased at 930° and an oxygen fugacity of log ƒO2 = −11·5. Further cooling and exsolution continued until the grain reached 662 °C and log ƒO2 = −19·0, producing distinct ilmenite lamellae.

Janggunite occurs as radiating groups of flakes, flower-like aggregates, colloform bands, dendritic or arborescenl masses in the cementation zone of the supergene manganese oxide deposits. The flakes average 0·05 mm. Colour black, lustre dull, streak brownish black to dark brown. Cleavage one direction perfect. H = 23, very fragile. Dmeas = 3·59, Dcalc = 3·58. Under reflected light anisotropic and bireflectant. No internal reflections. Etching reactions: positive - HC1, HNO3, SnCl2, H2O2, H2SO4 + H2O2. Chemical formula, on the basis of O = 14, or ideally . The mineral has an orthorhombic unit cell with a 9·324, b 14·05, c 7·956 Å, Z = 4, a:b:c = 0·663:1:0·566. Important diffraction lines are 9·34(s), 7·09(s), 4·62(m), 4·17(m), 3·547(s), 3·101(s), 2·597(w), 2·469(m), 1·863(w), 1·664(w), 1·525(m), 1·405(m), D.T.A. curve shows the endothermic peaks at 250–370°C and 955°C Infra-red absorption spectral curve shows vibrations at 515 cm−1, 545 cm−1, 1025 cm−1, and 3225 cm−1. The mineral and name have been approved before publication by the Commission on New Minerals and Mineral Names, I.M.A.